Dielectric resonator, dielectric notch filter, and dielectric filter

Abstract: The dielectric resonator of the invention comprises a cavity having a first threaded hole, a dielectric block provided in the cavity, a coupling device coupled with an electromagnetic field produced in the cavity, a frequency tuning member having a screw portion which is spirally engaged with the first threaded hole of the cavity, a distance between the dielectric block and the frequency tuning member being changed by rotating the frequency tuning member, for tuning a resonance frequency of the cavity depending on the distance, fixing means for fixing a relative positional relationship between the frequency tuning member and the cavity. The fixing means fixes the cavity and prevents the frequency tuning member from rotating due to a frictional force caused between the first threaded hole of the cavity and the screw portion of the frequency tuning member.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a dielectric resonator for a filter for selectively filtering a high-frequency signal having a desired frequency mainly used in a base station for a mobile communication system such as car telephones and portable telephones. More particularly, the present invention relates to a dielectric resonator according to the preamble of claims 1 and 2. Such a resonator is known from the document FR-A-2 649 538. 2. Description of the Related Art: In recent years, as the development of the mobile communication system such as car telephones, a notch filter using a dielectric resonator is increasingly demanded. Hereinafter, an exemplary conventional dielectric notch filter will be described with reference to figures. Figures 6A and 6B are external views of a conventional dielectric notch filter. Figure 6A is a top view and Figure 6B is a side view. In these figures, the dielectric notch filter includes cylindrical metal cavities 2401 , a base member 2402 , tuning members 2403 , and input/output terminals 2404 . The notch filter shown in Figure 6 has five resonators. A transmission line is formed in the base member 2402 and electromagnetically coupled with the respective dielectric resonators, so as to constitute the notch filter. Figure 7 shows the inside of a dielectric resonator used in the conventional dielectric notch filter shown in Figure 6 in a simplified manner. In the metal cavity 2401, a dielectric block 2501 and a coupling loop 2502 for electromagnetic coupling are provided. Figure 8 is a cross-sectional view showing an adjusting mechanism for adjusting the degree of electromagnetic coupling in the conventional dielectric resonator. As shown in Figure 8 , the adjusting mechanism includes a supporting member 2 for supporting the dielectric block 2501 , a loop 4a of the coupling loop 2502 , a ground part 4b of the coupling loop 2502 , a handle 4c for rotating the whole coupling loop 2502 , and a pole 5 of the coupling loop 2502 . The pole 5 is composed of a center conductor 5a and an insulator 5b . The base member 2402 includes a transmission line 7 serving as an inner conductor and outer conductors 8 . The transmission line 7 is supported by a supporting member 9 which is an insulator. In general, the dielectric block 2501 is formed integrally with and supported by the supporting member 2 using glass with a low melting point. The operation principle of the conventional dielectric resonator having the above-described construction will be described below. When the dielectric block 2501 and the coupling loop 2502 are held in the metal cavity 2401 and the transmission line 7 is connected thereto, an electromagnetic field is produced in the cavity 2401 . Thus, the conventional dielectric resonator has a resonance frequency corresponding to a resonant mode. The degree of electromagnetic coupling of the dielectric resonator is a critical parameter for determining the electric characteristic of the dielectric resonator. The degree of electromagnetic coupling is determined depending on the number of lines of magnetic force across the cross section of the coupling loop 2502 . That is, according to the conventional technique, the coupling loop 2502 is mechanically rotated by the handle 4c and hence the effective cross-sectional area is varied, so that the number of lines of magnetic force across the coupling loop 2502 is adjusted. In order to match the impedance of the dielectric resonator, the electric length of the coupling loop is precisely adjusted to be an odd-integer multiple of a quarter wavelength. However, the above-described prior art has the following drawbacks. (1) A complicated mechanism for mechanically rotating the coupling loop is required, and hence the number of components required is increased. (2) The means for impedance matching is limited, and the size of the coupling loop is greatly increased for lower frequencies. Also, since the coupling loop is small for higher frequencies, it is impossible to attain a higher degree of coupling. (3) In principle, the range of frequencies in which the impedance matching can be achieved is narrow. (4) In order to melt the glass for adhesion, a heating treatment to the dielectric member is required. The adhesive strength of glass is low, and the mechanical reliability is poor. As a result, the following problems arise. (1) The coupling loop is easily rotated due to vibration and impact, so that the degree of electromagnetic coupling is varied. (2) The production process is complicated. (3) The production cost is increased. SUMMARY OF THE INVENTION Thus, the present invention concerns a dielectric resonator as defined in the appended claims. Thus, the invention described herein makes possible the advantages of providing a tuning mechanism which is constructed with a smaller number of components, and (5) providing steep notch filter characteristics. These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a view showing an exemplary construction of a dielectric notch filter in the example of the invention. Figure 2 is a view showing another exemplary construction of a dielectric notch filter in the example of the invention. Figure 3 is a view showing an exemplary coupling between dielectric resonators in the example of the invention, resulting in a band pass filter. Figure 4 is a view showing an exemplary construction of a tuning mechanism in the example of the invention. Figure 5 is a view showing an exemplary construction of a tuning mechanism in the example of the invention. Figure 6A is a top view of a conventional dielectric notch filter, and Figure 6B is a side view of the conventional dielectric notch filter shown in Figure 6A . Figure 7 is a view showing the inside construction of the conventional dielectric resonator. Figure 8 is a view of an electromagnetic coupling mechanism of a conventional dielectric resonator in detail. Figure 1 shows a development view of the exploded construction of a dielectric notch filter in an example of the present invention. In Figure 1, the dielectric notch filter has a base member 1801 and a cover member 1802, a housing member 1803 for a transmission line 108 , and a pair of connector stands 1804 for supporting the input/output connectors 103. Holes 1805a - 1805e are provided in the metal cavities 101a - 101e, respectively. The metal cavities 101 have respective coupling loops 107a - 107e therein. One end of each of the coupling loops 107a - 107e is grounded to the corresponding one of the metal cavities 101a - 101e, and the other end thereof is led out through the corresponding one of the holes 1805a - 1805e. Each of the metal cavities 101a - 101e has rectangular openings having an aspect ratio of 1.0 to 2.0 as the top and bottom faces. The cover member 1802 has tuning members 104a - 104e for the respective dielectric resonators. The metal cavities 101a - 101e each having the above-described construction are arranged in one direction, and the base member 1801 and the cover member 1802 are integrally formed so as to close the top and bottom openings of the metal cavities 101a - 101e. The housing member 1803 constitutes a shielding metal for a high-frequency transmission line of triplate type, by vertically sandwiching the transmission line 108 . In the housing member 1803 , the transmission line 108 , the coupling adjusting lines 106a - 106e, and the reactance elements 110a - 110e are provided. As an example of such reactance elements 110a - 110e, an air-core coil with one end grounded is used in this example. With the above-described construction, it is possible to attain the following effects using the minimum number of necessary components. (1) It is possible to constitute a metal cavity 101 having a high value of Q for the above-described reasons. (2) It is possible to realize a transmission line with a lower power loss. (3) It is possible to easily adjust the inverter between resonators, by changing the point at which the coupling adjusting line 106 is connected. (4) It is possible to constitute a dielectric notch filter which is mechanically extremely sturdy. Instead of the construction of the metal cavity 101 shown in Figure 1 , a metal body member 1901 of a box-like shape and having a capacity of several cavities can be used and divided by partition plates 1902, and then the body member 1901 is closed by a cover member 1903 as shown in Figure 2 . The above-described example of the invention is described for a band rejection filter. In addition, the construction of the metal cavity of the invention can be applied to a band pass filter, and the like. Figure 3 schematically shows the construction of an exemplary band pass filter. Herein, the band pass filter includes coupling loops 107 and coupling windows 2001 . As described above, the method for adjusting the degree of electromagnetic coupling of the coupling loop, the impedance matching method, and the metal cavity construction can be used, and the same effects can be attained. In this example, a tuning mechanism can be provided for the metal cavity 101 . The tuning member in this example will be described with reference to Figures 4 and 5 . Figures 4 and 5 show exemplary constructions of the tuning member in this example. In Figures 4 and 5 , a disk-like metal tuning plate 2101 is integrally formed with a tuning screw 2102 . The cover member 1802 , lock nuts 2103 and 2201 have threaded center openings, respectively. By rotating the tuning screw 2102, the tuning plate 2101 can be moved upwardly or downwardly. In Figure 4 , the lock nut 2103 has a through hole for allowing a screw 2104 to pass, and the cover member 1802 has a threaded hole which is spirally engaged with the screw 2104. In Figure 5 , the lock nut 2201 has a threaded hole which is spirally engaged with the screw 2104 . The construction of the tuning mechanism shown in Figure 4 will be described. In this example, the cover member 1802 is provided with a thread at a position corresponding to the through hole in the lock nut 2103 . The resonance frequency of the dielectric resonator can be adjusted by upwardly or downwardly moving the tuning plate 2101 . In this example, the cover member 1802 is threaded so as to be spirally engaged with the thread of the tuning screw 2102 , so that the tuning plate 2101 can be upwardly and downwardly moved by rotating the tuning screw 2102. After the frequency is tuned by the above-described method, the tuning screw 2102 is locked by the lock nut 2103. At this time, with a slight gap (in the range of 0.1 mm to 1.0 mm) between the lock nut 2103 and the cover member 1802 , the through hole of the lock nut 2103 is aligned with the thread of the cover member 1802 , and the screw 2104 is attached from the above of the lock nut 2103 . By tightening the screw 2104 , the lock nut 2103 is pressed, so that the tuning screw 2102 can be positively locked. Another construction of the tuning mechanism shown in Figure 5 will be described. In this example, the lock nut 2201 is threaded so as to be spirally engaged with the thread of the screw 2104 . After the frequency is tuned, the screw 2104 is tightened by utilizing the thread of the lock nut 2201 , so that an upward force is applied to the lock nut 2201 , and hence the tuning screw 2102 can be positively locked.

Claims: A dielectric resonator comprising: a cavity cover (1802) having a first threaded hole; a dielectric block provided in the cavity; a coupling device coupled with an electromagnetic field produced in the cavity; a frequency tuning member (2101) having a screw portion (2102) which is spirally engaged with the first threaded hole of the cavity cover (1802), a distance between the dielectric block and the frequency tuning member being changed by rotating the frequency tuning member (2101), for tuning a resonance frequency of the cavity depending on the distance; fixing means (2103, 2104) for fixing a relative positional relationship between the frequency tuning member (2101) and the cavity cover (1802), wherein the fixing means (2103, 2104) fixes the cavity cover (1802) and prevents the frequency tuning member from rotating due to a frictional force caused between the first threaded hole of the cavity cover (1802) and the screw portion (2102) of the frequency tuning member (2101), the fixing means includes a lock nut (2103) and a fixing screw (2104), characterised in that the lock nut has a second threaded hole which is spirally engaged with the screw portion (2102) of the frequency tuning member (2101) and a through hole through which the fixing screw (2104) is passed, the cavity cover (1802) having a third threaded hole which is spirally engaged with the fixing screw (2104), and the fixing means applies a force in a direction in which the lock nut (2103) and the cavity cover (1802) come closer to each other by tightening the fixing screw (2104). A dielectric resonator comprising: a cavity cover (1802) having a first threaded hole; a dielectric block provided in the cavity; a coupling device coupled with an electromagnetic field produced in the cavity; a frequency tuning member (2101) having a screw portion (2102) which is spirally engaged with the first threaded hole of the cavity cover (1802), a distance between the dielectric block and the frequency tuning member being changed by rotating the frequency tuning member (2101), for tuning a resonance frequency of the cavity depending on the distance; fixing means (2201, 2104) for fixing a relative positional relationship between the frequency tuning member (2101) and the cavity cover (1802), wherein the fixing means (2201, 2104) fixes the cavity cover (1802) and prevents the frequency tuning member from rotating due to a frictional force caused between the first threaded hole of the cavity cover (1802) and the screw portion (2102) of the frequency tuning member (2101), the fixing means has a lock nut (2201) and a fixing screw (2104), characterised in that the lock nut (2201) has a fourth threaded hole which is spirally engaged with the screw portion (2102) of the frequency tuning member (2101) and a fifth threaded hole which is spirally engaged with the fixing screw (2104), and the fixing means applies a force in a direction in which the lock nut (2204) and the cavity cover (1802) are moved away from each other by tightening the fixing screw (2104).

Inventors: HATANAKA MASAMI, ISHIZAKI TOSHIO, NAKAMURA TOSHIAKI, SAKA YUJI, SATOH YUKI, HATANAKA, MASAMI, ISHIZAKI, TOSHIO, NAKAMURA, TOSHIAKI, SAKA, YUJI, SATOH, YUKI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: H01P1
IPC codes: H01P1, H01P7